This invention relates to a non-oxide-series-sintered ceramic body and a method for forming a conductive film on the surface of a non-oxide-series-sintered ceramic body.
It is common practice to form a conductive film on the surface of a sintered ceramic body so as to obtain a bond between a sintered ceramic body and a metallic member. It is possible to electroplate, for example, nickel on the conductive film and bond the nickel film to the metallic member by brazing, etc. The conventional method for forming such a conductive film comprises coating a metallized paste, consisting mainly of molybdenum powder and manganese powder, on the surface of a sintered body, and sintering it done in a reducing atmosphere. This method is successfully applied to an oxide-series-sintered ceramic body such as alumina, but cannot necessarily be applied to a non-oxide-series-sintered ceramic body such as silicon nitride, which has recently been highlighted in view of its excellent wear resistance and its high-temperature performance, because no reaction occurs between the metallized paste and the non-oxide-series-sintered ceramic body and because it is difficult to form a conductive film with better adhesion. As a method for forming a conductive film on the surface of the non-oxide-series-sintered ceramic body, an attempt is made to impregnate ammonium molybdate into the surface of a porous-sintered ceramic body consisting of silicon nitride obtained by, for example, a reactive sintering method and a reduce ammonium molybdate to form a conductive film on the surface of a ceramic body. Since the conductive film is comprised of molybdenum with a thermal expansion coefficient substantially equal to that of the silicon nitride ceramics, this method is effective in obtaining a bond between the sintered ceramic bodies. Where, however, a bond is to be obtained between the sintered ceramic body and the metallic member, such as a steel member in particular, debonding or cracks occur during and after a bonding period due to a difference in the thermal expansion coefficient between the molybdenum and the steel. As a result, an adequate bonding strength is not obtained.